Portable crimping apparatus currently in use in the industry for crimping electrical terminals onto conductors are typically powered by hydraulic or compressed air actuators or electric motors of the type requiring an external power source. One such crimping tool is the AMP Incorporated tool number 46110 which has a linear actuator which uses a combination of air and hydraulic power to provide the necessary crimping forces. This tool is constructed so that the motion of the movable die toward the fixed die is linear thereby providing a superior crimp relative to that produced by the scissors action type tools known in the industry. The linear actuator of this tool supplies about 3600 pounds of force to the piston rod. There is no mechanism for providing an additional mechanical advantage so that the 3600 pounds of force is made available and applied directly to the crimping die during its entire stroke, although such a large force is required for only a small portion of the stroke. Thus, the unit necessarily must be large enough to supply the full 3600 pounds on demand. An example of a scissors action type crimping tool is the AMP Incorporated tool number 314597-1 which utilizes an air cylinder to drive a wedge between a pair of pivoting links that have mating crimping die halves attached to their ends. The forces made available to the crimping dies by this scissors action can be varied somewhat by varying the surface of the wedge. While the degree of such variation is quite limited the linear actuator need not have the capability of delivering the full amount of required force directly to the crimping dies, but instead may deliver a smaller amount with the wedge and links providing the mechanical advantage to make up the difference. Therefore, a smaller linear actuator may be used, although it is still larger than is necessary. Additionally, the scissors action of this tool is not desirable for crimping. Another crimping tool is the AMP Incorporated tool number 69365 which utilizes an air cylinder to drive a wedge against a single pivotable link which, in turn, pushes against a ram having the movable die attached thereto. This arrangement provides about the same degree of flexibility as that of the tool 314597-1 described above, however, it has the disadvantage of being rather clumsy to handle because the axis of the air cylinder is offset from the axis of the crimping dies and therefor requires an additional handle for proper balance. This, of course, adds weight to the tool and makes it more bulky. In all of these cases the force needed to effect the crimp is not linear over the entire length of the stroke of the actuator, resulting in an actuator having a power output equal to or greater than the highest force required during the course of the crimp. What is needed is a linear action crimping tool having the capability to vary its mechanical advantage to correspond with the forces required during the crimping cycle.